Mobile communications system and routing management apparatus used in the mobile communications system

ABSTRACT

A mobile communications system is disclosed that includes a first local routing manager (LRM) providing a first network in which a mobile terminal is currently located, a second local routing manager (LRM) providing a second network in which a counterpart terminal communicating with the mobile terminal is currently located, and a home routing manager (HRM) managing correspondence between the unique home address of the counterpart terminal and the second network. The first LRM has a controller that acquires address information of the counterpart terminal from the second LRM, via the HRM, when the first LRM does not have the address information, and communication means that transmits the address information of the counterpart terminal to a router of a new cell in the first network when the mobile terminal moves into the new cell.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of and claims the benefit of priorityunder 35 U.S.C. §120 from U.S. Ser. No. 10/749,398 , filed Jan. 2, 2004,and claims the benefit of priority under 35 U.S.C. §119 from JapanesePatent Application No. 2003-003485, filed Jan. 9, 2003, the entirecontents of each which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention generally relates to a mobile communicationstechnique, and more particularly to a mobile communications system thatmanages mobility of a mobile terminal in a network and to a routingmanager used in the mobile communications system.

Various studies have been made on Internet Protocol (IP) based mobilecommunication networks.

FIG. 1 is an example of such an IP based mobile communications system.The system 100 includes a first network 102 managed by atelecommunication carrier to provide mobile telephone services, a secondnetwork 104 managed by the same or a different telecommunication carrierto provide mobile telephone services, and a third network 106, such asthe Internet, connecting the first and second networks 102 and 104.Signal transmission of a mobile terminal in the first network 102 ismanaged by a first local routing manager (LRMs) 108. The lower caseletter “s” denotes a sender, which in this case is the mobile terminal120. The lower case letter “r” described below denotes a receiver, whichin this example is a counterpart destination mobile terminal 136. It isneedless to say that the mobile terminal 120 and the counterpartdestination terminal 136 function as both senders and receivers duringtelecommunications.

In the first network 102, an anchor router (ANRs) 110 and access routers(ARs) 112 and 114 connected under the anchor router 110 are arranged.The access routers 112 and 114 have cells 116 and 118, respectively,which are prescribed geographic areas controlled by these accessrouters. The access routers 112 and 114 are capable of communicatingwith mobile terminals located in the associated cells. In the exampleshown in FIG. 1, the mobile terminal 120 is located in the cell 116 ofthe access router 112. ANRs 110 delivers or routes a received packet toaccess router 112 or 114 according to the routing management scheme ofLRMs 108. The LRMs 108 manages a table of received packets (TRP) thatdescribes how the address of the packet received at the ANRs 110 is tobe converted for routing the packet. In general, there is one or moreanchor routers in a network. When using multiple anchor routers, thenetwork is divided into multiple sections, and packet routing efficiencyis improved.

Similarly, signal transmission of a mobile terminal in the secondnetwork 104 is managed by a second local routing manager (LRMr) 122. Inthe second network 104, access router (oARr) 128 connected under anchorrouter (oANRr) 124, and access router (nARr) 130 connected under anchorrouter (nANRr) 126 are arranged. The lower case letters “o” and “n”denote old and new, respectively, which represent before and afterhandover between cells. The access routers 128 and 130 have cells 132and 134, respectively, which are prescribed geographic areas controlledby these access routers. The access routers 128 and 130 are capable ofcommunicating with mobile terminals located in the associated cells. Inthe example shown in FIG. 1, the counterpart terminal 136, which is incommunication with the mobile terminal 120, is located in the cell 132of the access router 128. Anchor routers 124 and 126 deliver or route areceived packet to the associated access routers 128 and 130, accordingto the routing management scheme of LRMr 122. The LRMr 122 manages atable of received packets (TRP) that describes how the address of thepacket received at each of the anchor routers is to be converted forrouting the packet.

The mobile communications system 100 also includes home routing manager(HRMr) 138. Home routing manager (HRMr) 138 manages the correspondencebetween the unique IP home address “IPhar” of the counterpart terminal136 and the address “ANRr.x” used in the network in which thecounterpart terminal 136 is currently located as a visitor. Home address“IPha” is an unchanging IP address assigned to each terminal, regardlessof which network the terminal is currently visiting. In the network, anIP routing address “IPra”, such as “AR.x”, is also used. This IP routingaddress is a temporary address assigned by the associated access routerto the terminal located in the cell. The mobile communications system100 further includes home routing manager (HRMs) 140, which manages thecorrespondence between the unique IP home address “IPhas” of the mobileterminal 120 and the local address “ANRs.x” used in the network in whichthe mobile terminal 120 currently exists.

FIG. 2 is sequence diagram showing a sequence carried out whentelecommunication is started between the mobile terminal 120 and thecounterpart destination terminal 136 in the mobile communications system100 shown in FIG. 1. First, as indicated by step 202, the mobileterminal 120 transmits a data packet addressed to the counterpartterminal 136, designated by the home address “IPhar”, to the accessrouter 112 to which the mobile terminal currently belongs. The accessrouter 112 refers to the table of sending packets (TSP) to determine towhich access router or anchor router the packet with address “IPhar” isto be transferred. If the table of sending packets defines the addressfor accessing the counterpart destination terminal 136, then the accessrouter 112 converts the address held in the data packet to the newaddress described in the table of sending packets in order to route thepacket.

If there is no information about the counterpart destination terminal136 in the table of sending packets, then the access router 112 queriesthe home routing manager (HRMr) 138, which manages the IP home address“IPhar” of the counterpart terminal 136, about the information of thecounterpart destination terminal 136, as indicated in step 204. Then, instep 206, the access router 112 acquires the address required to accessthe counterpart terminal 136. Since in the example shown in FIG. 1 thecounterpart destination terminal 136 is located in cell 132 controlledby access router 128 under the anchor router 124, the home routingmanager HRMr 138 manages the home address “IPhar” in association withaddress “oANRr.x” given under the anchor router 124. The latter addressis reported to the access router 112. Upon receiving the current localaddress, the access router 112 creates a new entry in the table ofsending packets so as to convert the home address “IPhar” of thecounterpart terminal 136 into address “oANRr.x” assigned under anchorrouter 124.

In FIG. 2, double arrows (such as step 202) represent a signaltransmission containing a data packet transmitted between the mobileterminal 120 and the counterpart terminal 136. The single arrows (suchas step 204) represent transmission of control signals that do notcontain substantial data packets.

Hereinafter, address “IPhar” of the data packet having arrived at theaccess router 112 is converted to address “oANRr.x”, and theaddress-converted packet is transmitted in the network, as in step 208.

Then, in step 210, the anchor router 124 converts the address “oANRr.x”of the received packet to “oARr.x”, based on the table of receivedpackets (TRP), and transmits the address-converted packet to the accessrouter 128 arranged under this anchor router 124. The contents of thetable of received packets (that is, converting “oANRr.x” to “oARr.x”)are defined by LRMr 122 that manages the locations and the mobility ofthe cellular terminals existing in the network 104. The access router128 gives the address “oARr.x” to the counterpart terminal 136 fortelecommunications when the counterpart terminal 136 has entered thecell 132, and records the correspondence between the local address andthe home address of the counterpart terminal 136 (indicating addressconversion from “oARr.x” to “IPhar”) in the table of received packets(TRP).

Accordingly, upon receiving the data packet addressed to “oARr.x”, theaccess router 128 converts this address to “IPhar” according to thetable TRP, and transmits the address-converted packet to the counterpartdestination terminal 136, as in step 212. In this manner, the datapacket transmitted from the mobile terminal 120 is correctly deliveredto the counterpart destination terminal 136.

Next, when the counterpart terminal 136 responds to the mobile terminal120, the access router 128 receives a data packet addressed to the homeaddress “IPhas” of the mobile terminal 120 in step 214. The subsequentprocedures are the same as those in steps 202 through 212. The accessrouter 128 checks the table of sending packets in order to convert thehome address “IPhas” of the mobile terminal 120 to the appropriateaddress. If there is information about the address conversion defined inthe transmission table TSP, the home address of the data packet isconverted to the local address indicated by the transmission table TSPfor further transmission.

If there is no information about address conversion of the mobileterminal 120 in the transmission table TSP, then the access router 128requests information about the mobile terminal 120 from the home routingmanager (HRMs) 140, which manages the IP home address “IPhas” of themobile terminal 120, as indicated in step 216. Then, the access router128 acquires address “ANRs.x”, which is given under the anchor router110 and managed in association with home address “IPhas”. The accessrouter 128 creates a new entry in the table of sending packets TSP so asto convert the home address “IPhas” of the mobile terminal 120 intoaddress “ANRs.x” assigned under anchor router 110.

Hereinafter, address “IPhas” of the data packet having arrived at theaccess router 128 is converted to address “ANRs.x”, and theaddress-converted packet is transmitted in the network, as in step 220.

Then, in step 222, the anchor router 110 converts the address “ANRs.x”of the received packet to “oARs.x”, based on the table of receivedpackets (TRP), and transmits the address-converted packet to the accessrouter 112 arranged under this anchor router 110. The contents of thetable of received packets (that is, converting “ANRs.x” to “oARs.x”) aredefined by LRMs 108 that manages the locations and the mobility of thecellular terminals existing in the network 102. The access router 112gives the address “oARs.x” to the mobile terminal 120 when the mobileterminal 120 has entered the cell 116 for telecommunication, and recordsthe correspondence between the local address and the home address of themobile terminal 120 (indicating address conversion from “oARs.x” to“IPhas”) in the table of received packets (TRP).

Accordingly, upon receiving the data packet addressed to “oARs.x”, theaccess router 112 converts this address to “IPhas” according to thetable TRP, and transmits the address-converted packet to the mobileterminal 120 located in the cell 116, as in step 224. In this manner,the data packet transmitted from the counterpart terminal 136 iscorrectly delivered to the mobile terminal 120.

Since when a data packet is relayed at each node, address conversion isconducted, rather than encapsulation, overhead can be prevented fromincreasing. Accordingly, packet transmission can be performedefficiently. In addition, in telecommunication between the mobileterminal and the counterpart terminal, only each other's home addressesare used, and the routing address (for example, “ARr.x”, “oARs.x”, etc.)containing the location information of the cellular terminal isconcealed in the network. Consequently, privacy of the user isprotected. Concerning the above-described type of mobile communicationssystem, see “Mobility Management Architecture for IP-based IMT NetworkPlatform”, M. Sawada, et al., IEICE Society Conference, September 2002.

FIG. 3 shows the communications sequence during handover of the mobileterminal 120 between cells, which could happen after the sequence shownin FIG. 2. In this example, the mobile terminal 120 currently located incell 116 and in communication with the counterpart terminal 136, ismoving to another cell.

To allow the handover of the mobile terminal 120, the tables of receivedpackets stored in the anchor router 110 and a new access router 114 haveto be updated so as to forward incoming packets addressed to the mobileterminal 120 to the new access router 114. The table of received packetsof the access router 114 may be updated when the access router 114assigns address “nARs.x” to the mobile terminal 120. The table ofreceived packets of the anchor router 110 is updated based on thenotification transmitted from the new access router 114 to the LRMs 108in step 301. The LRMs 108 instructs anchor router 110 to update thetable of received packets in step 303.

In addition to updating the table of received packets, the access router114 has to create a new entry in the table of sending packets TSP. Asindicated in step 305, when receiving data packets addressed to homeaddress “IPhar” of the counterpart terminal 136 from the mobile terminal120, the access router 114 searches in the table of sending packets.However, it is currently unknown to which address the home address“IPhar” of the counterpart terminal 136 be converted because there is nopast record of sending packets from this access router 114 to thecounterpart terminal 136.

Accordingly, in step 304, the access router requests the informationabout the counterpart terminal 136 from the home routing manager HRMr138 that manages the home address “IPhar” of the counterpart terminal136, if the table of sending packets does not have the information.Then, the access router 114 acquires information about the local addresscurrently used by the counterpart terminal 136 in step 306. Based on theinformation, the access router 114 creates a new entry representingaddress conversion of the home address “IPhar” of the counterpartterminal 136 into “oANRr.x” assigned under the anchor router 124.

When the new entry is recorded in the table of sending packets, the datapackets addressed to the counterpart terminal 136, which have beenbuffered in the access router 114, are transmitted to the anchor router124, as in step 308. Then, the data packets are forwarded to thecounterpart terminal 136 in steps 310 and 312.

However, this method has a problem because HRMe 138 is generally faraway from network 102, and therefore, the requesting and responding(steps 304 and 306) between the access router 114 and HRMr 138 arelikely to take a long time. This results in undesirable delay increating a new entry in the table of sending packets at the new accessrouter. Unless the new entry is recorded in the table of sendingpackets, the data packets buffered in the access router cannot betransmitted. This makes it difficult to carry out handover, whiletransmitting data packets continuously. Especially, since the requestingsequence from the access router 114 (such as steps 304 and 306) isstarted after the receipt of data packets transmitted from the mobileterminal 120 to the counterpart terminal 136, the data packets arebuffered in the access router 114 until the requesting sequence iscompleted and the table of sending packets is updated. It is a concernthat the buffering delay becomes undesirably long. In addition, as thetime required to update the table of sending packets becomes greater,the volume of data packets buffered in the access router 114 becomeslarge, and therefore, a large-capacity memory is required.

FIG. 4 shows a communications sequence during handover of thecounterpart terminal 136 between cells, which could also happen afterthe sequence shown in FIG. 2. In this example, the counterpart terminal136 is moving from cell 132 to another cell 134. If the handover isconducted between access routers under the same anchor router 124, thetables of received packets of the new access router 130 and the anchorrouter 124 can be updated using the same procedure as shown in steps 301through 306. In this case, the same problem as has been described inconnection with FIG. 3 occurs.

The handover sequence illustrated in FIG. 4 is one conducted betweenaccess routers under different anchor routers. In step 402, thecounterpart terminal 136 accesses the new access router 130. The accessrouter 130 creates a new entry in the table of received packets so as toassociate the local address “nARr.x” assigned by the access router 130with home address “IPhar” of the counterpart terminal 136.

Then, in step 404, the access router 130 requests LRMr 122 to update thetable of received packets stored in the new anchor router 126. Inresponse to the request, LRMr 122 and the new anchor router 126 updatethe tables of received packets so that address “nANRr.x” is associatedwith address “nARr.x” assigned by the access router 130, as in step 406.

Then, in step 408, LRMr 122 requests HRMr 138 to update the record so asto associate the home address “IPhar” of the counterpart terminal 136with address “nANRr.x” assigned under the new anchor router 126.

Then, in step 410, the HRMr 138 reports the updated correspondencebetween the home address “IPhar” of the counterpart terminal 136 and thenew local address “nANRr.x” assigned under the anchor router 126 to theaccess routers and other nodes that have queried HRMr 138 about thecounterpart terminal 136 in the past. In this particular example, theaccess router 112 has queried HRMr 138 in steps 204 and 206 in FIG. 2,and HRMr 138 stores this record. Upon receiving the report from HRMr138, the access router 112 updates the table of sending packets so as toconvert the home address “IPhar” of the counterpart terminal 136 into“nANRr.x”. In the subsequent process, the packets addressed to thecounterpart terminal 136 are correctly delivered to the counterpartterminal 136 located in the new cell.

However, because the table of sending packets of the access router (step410) is updated via HRMr 138, which in general is located far away fromthe first and second networks 102 and 104, time required to update thetable of sending packets may be undesirably increased. Unless the tableof sending packets of the access router 112 is promptly updated, anumber of data packets may be transmitted to the previous anchor router124 having functioned before the handover, depending on case. This mayresult in decreased transmission efficiency.

SUMMARY OF THE INVENTION

Therefore, it is an object of the present invention to overcome theabove-described problems in the conventional art, and to provide apacket routing management technique used in a mobile communicationssystem that allows the address conversion table used to convert theaddress of a packet to be updated promptly at each node, wheneverhandover occurs at a mobile terminal.

It is another object of the invention to provide a packet routingmanagement technique used in a mobile communications system that allowsprompt update of the address conversion table at each node wheneverhandover occurs at a counterpart mobile terminal.

To achieve the objects, in one aspect of the invention, a mobilecommunications system is provided. This mobile communications systemincludes:

a first local routing management apparatus (LRMs) that provides a firstnetwork and manages signal routing in the first network in which amobile terminal is currently located;

a second local routing management apparatus (LRMr) that provides asecond network and manages signal routing in the second network in whicha counterpart terminal communicating with the mobile terminal iscurrently located; and

a home routing management apparatus (HRMr) that manages correspondencebetween a unique home address of the counterpart terminal and the secondnetwork, wherein the first local routing management apparatus comprises:

-   (a) a controller that acquires address information about the    counterpart terminal from the second local routing management    apparatus, via the home routing management apparatus, when the first    local routing management apparatus does not have the address    information; and-   (b) communication means that transmits the address information about    the counterpart terminal to a first router of a new cell in the    first network when the mobile terminal moves into the new cell.

In another aspect of the invention, a local routing managementapparatus, which provides a first network and manages signal routing fora mobile terminal currently existing in the first network andcommunicating with a counterpart terminal located in a second network,is provided. The local routing management apparatus comprises:

a controller that acquires address information about the counterpartterminal from a second local routing management apparatus of the secondnetwork, via a home routing manager that managers correspondence betweena unique home address of the counterpart terminal and the secondnetwork, when the local routing management apparatus does not have theaddress information; and

communication means that receives an inquiry about the addressinformation of the counterpart terminal from a router of a new cell inthe first network when the mobile terminal moves into the new cell, andtransmits the address information about the counterpart terminal to therouter in response to the inquiry.

In still another aspect of the invention, a local routing managementapparatus providing a second network and managing signal routing for acounterpart terminal currently existing in the second network andcommunicating with a mobile terminal visiting in a first network isprovided. The local routing management apparatus comprises:

a controller that updates address information about the counterpartterminal in response to a request from a router of a new cell in thesecond network when the counterpart terminal moves into the new cell;

communication means that reports the updated address information of thecounterpart terminal directly to the first network, without passingthrough a home routing management apparatus that manages correspondencebetween a home address of the counterpart terminal and the secondnetwork; and

a storage that stores an address required to access the first network.

In yet another aspect of the invention, a home routing managementapparatus used in a mobile communications system including a first localrouting management apparatus providing a first network and managingsignal routing in the first network, and a second local routingmanagement apparatus providing a second network and managing signalrouting in the second network, is provided. The home routing managementapparatus comprises:

a controller that manages correspondence between a home address of acounterpart terminal and the second network in which the counterpartterminal currently exists, and acquires address information about thecounterpart terminal from the second network upon receiving an inquiryfrom the first local routing management apparatus;

a storage that stores an address required to access the first localrouting management apparatus; and

communication means that transmits the address information of thecounterpart terminal to the first local routing apparatus in response tothe inquiry.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, features, and advantages of the invention will becomemore apparent from the following detailed description when read inconjunction with the accompanying drawings, in which

FIG. 1 is a schematic diagram showing the overall structure of aconventional mobile communications system;

FIG. 2 is a sequence diagram of communications carried out in the mobilecommunications system shown in FIG. 1;

FIG. 3 is a sequence diagram carried out during handover of the mobileterminal in the mobile communications system shown in FIG. 1;

FIG. 4 is a sequence diagram carried out during handover of thecounterpart terminal in the mobile communications system shown in FIG.1;

FIG. 5 is a schematic diagram showing the overall structure of a mobilecommunications system according to an embodiment of the invention;

FIG. 6 is a block diagram of a local routing manager (LRM) used in themobile communications system shown in FIG. 5;

FIG. 7 is a block diagram of a home routing manager (HRM) used in themobile communications system shown in FIG. 5;

FIG. 8 is a sequence diagram of communications carried out in the mobilecommunications system shown in FIG. 5 according to an embodiment of theinvention;

FIG. 9 is a sequence diagram carried out during handover of the mobileterminal in the mobile communications system shown in FIG. 5 accordingto an embodiment of the invention; and

FIG. 10 is a sequence diagram carried out during handover of thecounterpart terminal in the mobile communications system shown in FIG. 5according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is described in detail below in conjunction withFIG. 5 through FIG. 10.

FIG. 5 schematically illustrates the overall structure of a mobilecommunications system according to an embodiment of the invention. Themobile communications system 500 includes a first network 502 thatprovides mobile telephone services managed by a telecommunicationcarrier, a second network 504 that provides mobile telephone servicesmanaged by the same or a different telecommunication carrier, and athird network 506, such as the Internet, connecting the first and secondnetworks 502 and 504. Signal transmission of a mobile terminal in thefirst network 502 is managed by a first local routing manager (LRMs)508.

In the first network 502, an anchor router (ANRs) 510 and access routers(ARs) 512 and 514 connected under the anchor router 510 are arranged.The access routers 512 and 514 have cells 516 and 518, respectively, andthey are capable of communicating with mobile terminals located in theassociated cells. In the example shown in FIG. 5, the mobile terminal520 is located in the cell 516 of the access router 512. The ANRs 510delivers or routes a received packet to access router 512 or 514according to the routing management scheme of LRMs 508. The LRMs 508manages a table of received packets (TRP) that describes how the addressof the packet received at the ANRs 510 is to be converted for routingthe packet. In the embodiment, the LRMs 508 manages not only the tableof received packets, but also information about the tables of sendingpackets of the access routers 512 and 514, which differs from theconventional local routing manager LRM.

Similarly, signal transmission of a mobile terminal in the secondnetwork 504 is managed by a second local routing manager (LRMr) 522. Inthe second network 504, access router (oARr) 528 connected under anchorrouter (oANRr) 524, and access router (nARr) 530 connected under anchorrouter (nANRr) 526 are arranged. The access routers 528 and 530 havecells 532 and 534, respectively, and they are capable of communicatingwith a mobile terminal located in the associated cells. In the exampleshown in FIG. 5, the counterpart mobile terminal 536 which is incommunication with the mobile terminal 520 is located in the cell 532 ofthe access router 528. Anchor routers 524 and 526 deliver or route areceived packet to the associated access routers 528 and 530, accordingto the routing management scheme of LRMr 522. Similar to the LRMs 508,the LRMr 522 manages not only a table of received packets (TRP) thatdescribes how the address of the packet received at this anchor routeris to be converted for packet routing, but also the tables of sendingpackets (TSP) of the access routers arranged under this anchor router.

The mobile communications system 500 also includes home routing manager(HRMr) 538, which manages the correspondence between the unique IP homeaddress “IPhar” of the counterpart terminal 536 and the local routingmanager (LRMr) 522 that manages the network in which the counterpartmobile terminal 536 is currently located as a visitor. This arrangementis different from the conventional HRMr 138 that manages thecorrespondence between the home address “IPhar” of the counterpartterminal and the address information “oANRr.x” used in the network whichthe counterpart terminal is currently visiting. The mobilecommunications system 500 further includes home routing manager (HRMs)540, which manages the correspondence between the unique IP home address“IPhas” of the mobile terminal 520 and the local routing manager LRMs508 that manages the network which the mobile terminal 520 is currentlyvisiting.

FIG. 6 is a block diagram of the local routing manager (LRM) applicableto the mobile communications system 500 according to the embodiment. Thediagram of FIG. 6 shows the major elements of a LRM 600. The functionsof the local routing manager (LRM) 600 are in common between the firstand second LRMs 508 and 522 shown in FIG. 5; however, they are managingdifferent terminals. The LRM 600 has a communication interface 602,which interfaces communication with other nodes in the mobilecommunications system. Examples of such nodes include access routers(AR), anchor routers (ANR), home routing managers (HRM), and other localrouting managers (LRM). The LRM 600 has a controller 604 that controlsthe entire operation of the components of the LRM 600, and a cache table606 including a table of received packets (TRP) 608 and a table ofsending packets (TSP) 610. The LRM 600 also has a storage 612 thatstores information about those access routers that have queried the LRM600 in the past, as well as address information required to access othernodes, such as other local routing managers.

The contents of the table of received packet 608 controlled by thecontroller 604 include information indicating that, for example, packetsaddressed to the mobile terminal 520 currently located under the anchorrouter 510 are to be forwarded to the access router 512. To be moreprecise, the table of received packets 608 defines an address conversiontable defining how the address of a packet received at the anchor router510 is to be converted. The cache table 606 also includes a table ofsending packets 610, which has contents similar to the table of sendingpackets of the access router 512.

FIG. 7 is a block diagram of the home routing manager (HRM) 700applicable to the mobile communications system 500 according to theembodiment. The diagram of FIG. 7 shows the major elements of the HRM700. The functions of the home routing manager (HRM) 700 are in commonbetween the HRMr 538 and HRMs 540 shown in FIG. 5; however, they managedifferent mobile terminals. The HRM 700 has a communication interface702, which interfaces communication with another node, such as an LRM,in the mobile communications system 500. The HRM 700 has a controller704 that controls the entire operation of the components of the HRM 700,and a management table 706. The HRM 700 also has a storage 712 thatstores address information required to access other nodes, such as LRMs,that have queried the HRM 700 in the past.

The contents of the management table 706 include correspondence betweena unique home address of each terminal (such as the mobile terminal 520or the counterpart terminal 526) and the LRM that manages the networkwhich the terminal with the home address is currently visiting. If HRM700 is HRMr 538 shown in FIG. 5, the management table 706 manages thecorrespondence between the unique home address “IPhar” of thecounterpart terminal 536 and the LRMr 522 than manages the network 504which the counterpart terminal 536 is currently visiting.

FIG. 8 is a sequence diagram showing the operations carried out in themobile communications system 500 shown in FIG. 5. First, in step 802, tostart telecommunication with the counterpart terminal 536, the mobileterminal 520 transmits a data packet addressed to the counterpartterminal 536, designated by the home address “IPhar”, to the accessrouter 512 to which the mobile terminal 520 currently belongs. Theaccess router 512 searches the table of sending packets (TSP) todetermine to which address the home address “IPhar” of the counterpartterminal 536 is to be converted. If the table of sending packets definesthe address of the access router or another node for accessing thecounterpart terminal 536, then the access router 512 converts the homeaddress held in the data packet to the new address described in thetable of sending packets to route the packet.

In step 804, if there is no information about the counterpartdestination terminal 536 in the table of sending packets, then theaccess router 512 queries the local routing manager (LRMs) 508, whichmanages the first network 502, about the information of the counterpartdestination terminal 536. If the LRMs 508 has the requested information,that information is immediately returned to the access router 512.

In FIG. 8, double arrows (such as step 802) represent signaltransmissions containing a data packet transmitted between the mobileterminal 520 and the counterpart terminal 536. The single arrows (suchas step 804) represent transmission of control signals that do notcontain substantial data packets.

If the LRMs 508 does not have information about the counterpartdestination terminal 536, the LRMs 508 inquires about the information byquerying the HRMr 538 that manages the home address “IPhar” of thecounterpart terminal 536, as indicated in step 806. At this time, theaddress required to respond to the access router 512 is stored in thestorage 612 under the control of the controller 604. The informationabout the counterpart terminal 536 is relevant to the table of sendingpackets (TSP) of the access router 512, which is also related to thetable of sending packets TSP of the LRMs 508. The operations ofsearching for the information about the counterpart terminal 536 in thetable of sending packets 610, and providing or inquiring aboutinformation based on the search results, are carried out under thecontrol of the controller 604. Upon receiving the inquiry from the LRMs508, the HRMr 538 refers to the management table 706 under the controlof controller 704, and finds that the counterpart terminal 536 with thehome address “IPhar” is currently visiting the network 504 managed bythe LRMr 522.

Then, by further querying the LRMr 522 specified based on thecorrespondence defined in the management table of the HRMr 538 in step808, address “oANRr.x” required to access the counterpart terminal 536is found. This address is transmitted to the LRMs 508 via the HRMr 538in steps 810 and 812. At this time, LRMr 522 stores in the storage 612an address required to access the LRMs 508 that has transmitted theinquiry about the counterpart terminal 536. When receiving the address“oANRr.x” for accessing the counterpart terminal 536, the LRMs 508writes this address “oANRr.x” in the table of sending packets 610 inassociation with the home address “IPhar” of the counterpart terminal536. Then, in step 814, the address “oANRr.x” for accessing thecounterpart terminal 536 is transmitted to the access router 512, whichoriginally inquired about the information. The access router 512 updatesthe table of sending packets, creating a new entry.

Then, in step 818, the subsequent packets incoming to the access router512 are transmitted to the anchor router 524 according to the table ofsending packets. The packets are further forwarded to the access router528 arranged under the anchor router 524, and finally delivered to thecounterpart terminal 536, as shown in steps 820 and 822.

Next, explanation is made of the procedure performed when thecounterpart terminal 536 responds to the mobile terminal 520, which isthe same as performed in steps 802 through 822. Namely, in step 824, thecounterpart terminal 536 transmits a data packet addressed to the mobileterminal 520, designated by the home address “IPhas”, to the accessrouter 528 to which the counterpart terminal 536 currently belongs. Theaccess router 528 searches in the table of sending packets (TSP) for theinformation corresponding to the home address “IPhas” of the mobileterminal 520. In this example, the TSP does not have the informationassociated with “IPhas”.

Then, in step 826, if there is no information about the mobile terminal520 in the table of sending packets, then the access router 528 queriesthe local routing manager (LRMr) 522, which manages the second network504, about the information of the mobile terminal 520. If the LRMr 522has the requested information, that information is immediately returnedto the access router 528.

If the LRMr 522 does not have the information about mobile terminal 520,the LRMr 522 queries the HRMs 540, which manages the home address“IPhas” of the mobile terminal 520, about that information, as indicatedin step 828. Upon receiving the inquiry from the LRMr 522, the HRMs 540refers to the management table 706 under the control of controller 704,and finds that the mobile terminal 520 with the home address “IPhas” iscurrently visiting the network 502 managed by the LRMs 508.

Then, in step 830, by further querying the LRMs 508 specified based onthe correspondence defined in the management table of the HRMs 540,address “ANRs.x” required to access the mobile terminal 520 is found.This address is transmitted to the LRMr 522 via the HRMs 540, as shownin steps 832 and 834. When receiving the address “ANRs.x” for accessingthe mobile terminal 520, the LRMr 522 writes this address “ANRs.x” inthe table of sending packets 610 in association with the home address“IPhas” of the mobile terminal 520.

Then, in step 836, the address “ANRs.x” for accessing the mobileterminal 520 is transmitted to the access router 528, which originallyinquired about the information. The access router 528 updates the tableof sending packets, creating a new entry.

Then, in step 840, the subsequent packets incoming to the access router528 are transmitted to the anchor router 510 according to the table ofsending packets. The packets are further forwarded to the access router512 arranged under the anchor router 510, and finally delivered to themobile terminal 520, as shown in steps 842 and 844.

FIG. 9 illustrates the communication sequence performed during handoverof the mobile terminal 520, which is moving from cell 516 to anothercell 518, while being in communication with the counterpart terminal536, in the mobile communications system 500 shown in FIG. 5.

To allow the handover of the mobile terminal 520, the tables of receivedpackets stored in the anchor router 510 and a new access router 514 haveto be updated so as to forward incoming packets addressed to the mobileterminal 520 to the new access router 514. The table of received packetsof the access router 514 may be updated when the access router 514assigns address “nARs.x” to the mobile terminal 520.

The table of received packets of the anchor router 510 can be updatedwhen the access router 514 receives a signal from the mobile terminal520 from the new cell 518, as indicated in step 902.

In step 904, in responding to the signal from the mobile terminal 520,the access router 514 reports the necessity of updating the table ofreceived packet to the LRMs 508. Then, in step 906, the LRMs 508instructs the anchor router 510 to update the table of received packet.

The new access router 514 has to create a new entry in the table ofsending packets, in addition to updating the table of received packets.

In step 910, the access router 514 queries the LRMs 508, which managesthe network 502 to which the access router 514 belongs, aboutinformation of the counterpart terminal 536. Since the LRMs 508 hasalready created the entry about the counterpart terminal 536 in step 812shown in FIG. 8, the LRMs 508 has the address “oANRr.x” required toaccess the counterpart terminal 538.

Accordingly, the address “oANRr.x” is transmitted to the access router514 that has made the inquiry in step 912. The access router creates anew entry in the table of sending packets so as to convert the homeaddress “IPhar” of the counterpart terminal 536 to “oANRr.x”.

Then, in step 914, data packets addressed to the counterpart terminal536 are transmitted from the mobile terminal 520 to the access router514. The data packets are forwarded to the counterpart terminal 536, viathe anchor router 524 and the access router 528, as shown in steps 916,918, and 920.

This process is efficient, as compared with the conventional methodshown in FIG. 3. In the conventional method, when the mobile terminalhas moved to a new cell, the new access router receives the packets fromthe mobile terminal, and buffers the packets while querying the HRMrabout information of the counterpart terminal. After the informationabout the counterpart terminal is acquired by the access router, thebuffered packets are transmitted to the counterpart terminal. Thisconventional technique takes a long time every time for handover tooccur.

In contrast, with the method of this embodiment, the access router ofthe new cell has already acquired information about the counterpartterminal and prepared the table of sending packets before the datapackets addressed to the counterpart terminal are transmitted from themobile terminal to this new access router. Accordingly, the new accessrouter can transmit the data packets immediately to the counterpartterminal upon receiving the data packets. Unlike HRMr 538, the LRMs 508is capable of communicating with the nodes located in the first network502 very quickly. During the handover of the mobile terminal 520, thenew access router can promptly create a new entry in the table ofsending packets by simply querying the LRMs 508 that manages the network502, without communicating with the more distant HRMs 538 or othernodes. Since the table of sending packets containing the entry for thecounterpart terminal is prepared before substantial data packets aretransmitted from the mobile terminal, it is not necessary to buffer thedata during the handover.

FIG. 10 shows a communication sequence during handover of thecounterpart terminal 536 between cells, which could also happen afterthe sequence of FIG. 8 in the mobile communication system shown in FIG.5. In this example, the counterpart terminal 536 is moving from cell 532to another cell 534. If the handover is conducted between access routerscontrolled under the same anchor router 524, the tables of receivedpackets of the new access router and the anchor router 524 can beupdated using the same procedure as shown in FIG. 9, and explanation forit is omitted.

The handover sequence illustrated in FIG. 10 is one conducted betweenaccess routers under different anchor routers. In step 1002, thecounterpart terminal 536 accesses the new access router 530. The accessrouter 530 creates a new entry in the table of received packets so as toassociate the local address “nARr.x” assigned by the access router 530with home address “IPhar” of the counterpart terminal 536.

Then, in step 1004, the access router 530 requests LRMr 522 to updatethe table of received packets stored in the new anchor router 526. Inresponse to the request, LRMr 522 and the new anchor router 526 updatethe tables of received packets so that address “nANRr.x” is associatedwith address “nARr.x” assigned by the access router 530, as in step1006.

Then, in step 1008, LRMr 522 requests LRMs 508 to update the record soas to associate the home address “IPhar” of the counterpart terminal 536with address “nANRr.x” assigned under the new anchor router 526. In thisexample, LRMs 508 has queried LRMr 522 about the counterpart terminal536, and the LRMr 522 stores the record.

Then, in step 1010, the LRMs 508 reports the updated correspondencebetween the home address “IPhar” of the counterpart terminal 536 and thenew local address “nANRr.x” assigned under the anchor router 526, to theaccess routers and other nodes that have queried LRMs 508 about thecounterpart terminal 536 in the past. In this particular example, theaccess router 512 has queried LRMs 508 in step 804 of FIG. 8, and LRMs508 has stored this record. Upon receiving the report from the LRMs 508,the access router 512 updates the table of sending packets so as toconvert the home address “IPhar” of the counterpart terminal 536 into“nANRr.x”. In the subsequent process, the packets addressed to thecounterpart terminal 536 are correctly delivered to the counterpartterminal 536 located in the new cell 534.

In this manner, during the handover of the counterpart terminal 536, thetable of sending packets can be updated promptly, without passingthrough a distant node, such as HRMr 538. This arrangement isadvantageous, as compared with the conventional technique shown in FIG.4.

In the above-described embodiment, prior to handover occurring at themobile terminal or the counterpart terminal, the local router manger LRMalready holds information required for a new access router to update thetable of sending packets when the mobile station or the counterpartterminal is moving to the corresponding new cell. Such information issaved in the LRM prior to the handover, for example, when a link isestablished between the mobile terminal and the counterpart terminal.Since the local routing manager LRM locally manages the mobility of theterminals existing in its network, it is capable of communicating with anode in the network very quickly. The access router involved in handovercan acquire necessary information by simply querying the local routingmanager LRM that manages the network locally, and updating the table ofsending packets promptly. As long as a cellular terminal moves betweencells within the same network, any access router controlling a new cellqueries the same LRM. Accordingly, it becomes unnecessary for the systemto query a distant home routing manager HRM, thereby avoiding a slowresponse every time handover occurs.

In addition, the home routing manager HRM manages correspondence betweena home address unique to a cellular terminal and a local routing managerLRM in which the cellular terminal currently exists. This arrangementdiffers from the conventional HRM that manages the correspondencebetween the home address of a cellular terminal and a local addressrequired to access the cellular terminal. The address required to accessthe cellular terminal is a routing address to an anchor router, such as“ANRr.x” or “ANRs.x”.

In general, required anchor routers vary depending on the positionalrelation between the mobile terminal and the counterpart terminal. Asingle mobile terminal A may communicate with multiple counterpartterminals via multiple anchor routers, depending on the case. In thiscase, the conventional HRM has to manage addresses of the multipleanchor routers for the mobile terminal A. In contrast, the home routingmanager HRM according to the embodiment simply manages thecorrespondence between a home address and a LRM, regardless of thenumber of anchor routers arranged under this LRM. Consequently, theworkload on the HRM can be reduced.

In conclusion, in the mobile communications system of the presentinvention, the address conversion table used to convert the routingaddress of a signal at each node can be updated and prepared promptlyupon detecting handover at a mobile terminal or a counterpart terminal.

This patent application is based on and claims the benefit of theearlier filing date of Japanese Patent Application No. 2003-003485 filedJan. 9, 2003, the entire contents of which are hereby incorporated byreference.

1. A mobile communications system including: a first local routingmanagement apparatus that provides a first network and manages signalrouting in the first network in which a mobile terminal is currentlylocated; a second local routing management apparatus that provides asecond network and manages signal routing in the second network in whicha counterpart terminal communicating with the mobile terminal iscurrently located; and a home routing management apparatus that managescorrespondence between a unique home address of the counterpart terminaland the second network, wherein the first local routing managementapparatus comprises: a controller that acquires address informationabout the counterpart terminal from the second local routing managementapparatus, via the home routing management apparatus, when the firstlocal routing management apparatus does not have the addressinformation; and communication means that transmits the addressinformation about the counterpart terminal to a router of a new cell inthe first network, in response to a request from the router, when themobile terminal moves into the new cell.
 2. A local routing managementapparatus providing a first network and managing signal routing for amobile terminal currently existing in the first network, the mobileterminal communicating with a counterpart terminal located in a secondnetwork, the local routing management apparatus comprising: a controllerthat acquires address information about the counterpart terminal from asecond local routing management apparatus of the second network, via ahome routing manager that managers correspondence between a unique homeaddress of the counterpart terminal and the second network, when thelocal routing management apparatus does not have the addressinformation; and communication means that receives an inquiry about theaddress information of the counterpart terminal from a router of a newcell in the first network when the mobile terminal moves into the newcell, and transmits the address information of the counterpart terminalto the router in response to the inquiry.
 3. The local routingmanagement apparatus of claim 2, wherein the communication meanstransmits the address information to the router before actual data aretransmitted from the mobile terminal to the counterpart terminal.
 4. Thelocal routing management apparatus of claim 2, wherein the controllercreates a new entry for the address information of the counterpartterminal and records the entry in a table of sending packets.
 5. A localrouting management apparatus providing a second network and managingsignal routing for a counterpart terminal currently existing in thesecond network and communicating with a mobile terminal visiting in afirst network, the local routing management apparatus comprising: acontroller that updates address information about the counterpartterminal in response to a request from a router of a new cell in thesecond network when the counterpart terminal moves into the new cell;communication means that reports the updated address information of thecounterpart terminal directly to the first network, without passingthrough a home routing management apparatus that manages correspondencebetween a home address of the counterpart terminal and the secondnetwork; and a storage that stores an address required to access thefirst network.
 6. A home routing management apparatus used in a mobilecommunications system including a first local routing managementapparatus providing a first network and managing signal routing in thefirst network, and a second local routing management apparatus providinga second network and managing signal routing in the second network, thehome routing management apparatus comprising: a controller that managescorrespondence between a home address of a counterpart terminal and thesecond network in which the counterpart terminal currently exists, andacquires address information about the counterpart terminal from thesecond network upon receiving an inquiry from the first local routingmanagement apparatus; a storage that stores an address required toaccess the first local routing management apparatus; and communicationmeans that transmits the address information of the counterpart terminalto the first local routing apparatus in response to the inquiry.
 7. Apacket routing method used in a mobile communications system including afirst local routing manager providing a first network in which a mobileterminal is currently located, a second local routing manager providinga second network in which a counterpart terminal communicating with themobile terminal is currently located, and a home routing managermanaging correspondence between a unique home address of the counterpartterminal and the second network, the method comprising the steps of:acquiring, at the first local routing manager, address information aboutthe counterpart terminal from the second local routing manager specifiedbased on the correspondence managed by the home routing manager; andacquiring, at a first router in a new cell in the first network, theaddress information of the counterpart terminal from the first localrouting manager when the mobile terminal moves into the new cell.
 8. Themethod of claim 7, wherein the first router acquires the addressinformation of the counterpart terminal before the first router receivesan actual packet transmitted from the mobile terminal to the counterpartterminal.
 9. A packet routing method used in a mobile communicatessystem including a first local routing manager providing a first networkin which a mobile terminal is currently located, a second local routingmanager providing a second network in which a counterpart terminalcommunicating with the mobile terminal is currently located, and a homerouting manager managing correspondence between a unique home address ofthe counterpart terminal and the second network, the method comprisingthe steps of: acquiring, at the first local routing manager, addressinformation about the counterpart terminal from the second local routingmanager based on a request from a first router of a cell in which themobile terminal is located; updating, at the second local routingmanager, the address information of the counterpart terminal based on arequest from a second router of a new cell in the second network whenthe counterpart terminal moves into the new cell; reporting the updatedaddress information of the counterpart terminal to the first localrouting manager; and instructing the first router to update the addressinformation of the counterpart terminal.
 10. The method of claim 9,further comprising the step of: storing, at the second local routingmanger, an address required to access the first local routing manager.